With respect to the synthesis of organohalosilanes, E. G. Rochow first disclosed direct reaction between metallic silicon and organohalide in the presence of a copper catalyst. See U.S. Pat. No. 2,380,995 and J. Am. Chem. Soc., 67, 963 (1945), “The direct synthesis of organosilicon compounds.” Further, J. Am. Chem. Soc., 67, 1772 (1945), “The direct synthesis of phenylchlorosilanes” reports that the contact mass is useful in the synthesis of phenylsilanes. After these reports, copper catalysts are acknowledged as prevailing catalysts in the organohalosilane synthesis by direct reaction of metallic silicon with organohalide. Since then, there have been reported a number of research works relating to various co-catalysts used together with copper catalysts, copper catalysts themselves and their treatment, reactors, additives used during reaction, and the like. All prior art investigations relate to copper catalyzed reactions.
On the other hand, tin serves as a catalyst in the contact mass for organohalosilane direct synthesis reaction, but in fact, tin is used solely as a co-catalyst for promoting reaction when copper is used as the main catalyst. For instance, U.S. Pat. No. 4,500,724 and JP-B 1-40035 disclose use of tin for methylhalosilane synthesis, JP-B 33-1370 discloses tin or tin alloys for phenylsilane synthesis, and JP-B 32-4570 discloses tin tetrahalides. No reference has been made to the contact masses in which the copper catalyst is absent or the copper catalyst is present in minor amounts, but not used as the main catalyst.
No substantial problems have arisen as long as the reaction deals with only methylhalosilanes. As silicone resins become diversified, there is an increasing demand for organohalosilanes having other organic groups such as phenyl. Synthesis of such organohalosilanes is carried out, as a matter of course, by direct reaction of metallic silicon with chlorobenzene in the presence of copper catalysts. The reaction with such organohalides having low reactivity suffers from the problems that the reaction temperature must be elevated (to about 400 to 600° C.), large amounts of by-products such as biphenyls and carbon form to complicate post-treatment, and the percent conversion of silicon to silane is very low despite a very large amount of the catalyst used.